System for multiple point simultaneous initiation of explosive charges

ABSTRACT

1. A system for controlling the geometry of a detonation shock wave applied to an explosive charge which comprises; a piezoelectric element having a first face and a second face and adapted to generate a voltage between said faces when stressed, explosive actuated means for applying a substantially instantaneous uniform compressive load to said element to produce a rapidly developing output voltage between said first face and said second face, a shunting resistor connected between said faces to short circuit slowly developing voltages, a plurality of electroresponsive detonators also connected across the first face and the second face, and a plurality of limiting resistors each connected in series with a respective one of said detonators to promote simultaneity of initiation of said detonators.

United States Patent [72] Inventor Richard H. F. Stresau Washington Grove, Md. [21] Appl. No. 667,302 [22] Filed June 21,1957 [45] Patented June 29, 1971 [73] Assignee The United States of America a represented by the Secretary of the Navy [54] SYSTEM FOR MULTIPLE POINT SIMULTANEOUS INITIATION 0F EXPLOSIV E CHARGES 9 Claims, 2 Drawing Figs.

[52] [1.8. CI l02/70.2 A, 102/28 R [51] 1nt.Cl ..F42c 11/02, F42c 15/40, F42d 1/04 [50] Field of Search 102/70.2, 72, 28

[56] References Cited UNITED STATES PATENTS 1,791,716 2/1931 Davis 102/72X 2,452,072 10/1948 Schatz 102/72 X 277,052 11/1951 Paso 102/70.2 G

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Thornas H. Webb Attorneys-Q. E. Hodges and Q. B. Warner CLAIM: l. A system for controlling the geometry of a detonation shock wave applied to an explosive charge which comprises; a piezoelectric element having a first face and a second face and adapted to generate a voltage between said faces when stressed, explosive actuated means for applying a substantially instantaneous uniform compressive load to said element to produce a rapidly developing output voltage between said first face and said second face, a shunting resistor connected between said faces to short circuit slowly developing voltages, a plurality of electroresponsive detonators also connected across the first face and the second face, and a plurality of limiting resistors each connected in series with a respective one of said detonators to promote simultaneity of initiation of said detonators,

SYSTEM FOR MULTIPLE POINT SIMULTANEOUS INITIATION OF EXPLOSIVE CHARGES The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a system for multiple point simultaneous initiation of explosive charges and is more particularly concerned with a detonating system in which a plurality of detonators are simultaneously actuated by a voltage generated across the faces of a piezoelectric element in response to the application of a compressive load thereto.

Multiple point simultaneous initiation of an explosive results in many novel and desirable effects. For example, the performance of shaped charges and the control of fragmentation of bombs, projectiles or the like are improved if the geometry of the detonation shock waves is controlled by simultaneously initiating a plurality of detonators which are distributed at several points about an explosive charge. Since the detonation velocity of the high explosives used in modern ordnance devices ranges from about 6,000 to 8,000 meters per second, it is apparent that the scatter in the initiation time of the detonators must not be greater than a few microseconds in order to maintain the desired shape of the detonation wave.

There are many electrical circuits capable of delivering a pulse simultaneously to a plurality of detonators connected in series or parallel. It is generally considered advisable to deliver more than enough energy to initiate the detonators within a very short time in order to minimize the effect of variations in the sensitivity of the individual detonators. A rather high voltage is required to deliver this energy. In the past, these high voltages have been developed by expensive and bulky rotating electrical machinery, multicell batteries, vibrators, and electronic devices.

It is therefore an object of this invention to provide a simple detonating system for controlling the shape of the detonating shock wave which system has not moving parts and'is less bulky than the detonating systems of the prior art.

Another object of this invention is to provide a novel, multiple point detonating system wherein all the components are extremely resistant to deterioration and possess a long shelf life.

Still another object of this invention is to provide an explosive initiated detonator fuse which may be actuated by direct mechanical stab, flame, or electricity.

Another object is to provide a system for multiple point initiation of an explosive charge which system includes a piezoelectric voltage generating element and an explosive actuated means for rapidly compressing the element.

An even further object is to provide a new and novel electrically operated detonator having a plurality of sequentially initiated layers of explosive material which is ignited by an electrical arc discharge through an appropriate layer of explosive material.

Yet another object is to provide a detonator which has several layers of explosive material and which is initiated by an electric spark discharge between a lead wire and the casing of the detonator across a selected explosive layer having a predetermined dielectric strength.

An even further object is to provide a detonator which may be armed by a high energy low voltage pulse and initiated by a low energy high voltage pulse.

It is a primary object of the present invention to provide means for the simultaneous detonation of a plurality of detonators distributed throughout the body of an explosive charge.

These and many other objects will become more apparent when the following specification is read in conjunction with the attendant drawings in which:

FIG. 1 is a longitudinal section of the piezoelectric fuse ele ment arranged with the detonating circuit therefor in accordance with the teachings of the present invention; and

FIG. 2 is a longitudinal section of one of the detonators shown schematically in FIG. 1.

Referring now to FIG. 1, the piezoelectric fuse element is composed of a steel charge holder, or cup, 11 having a bore 28 at its base through which an explosive initiator wire 12, insulated therefrom, extends into the interior of the cup 11 which is filled with an explosive charge 13. The wire 12 is shown connected to a resistance element 10 to illustrate a method of initiating charge 13 electrically; but, the mode of initiating the charge forms no part of this invention and it may also be initiated by direct mechanical stab, by flame, or by any other igniting means conventionally employed in the art.

A plurality of discs 14 are stacked above the mouth of the cup 11, these discs are preferably composed of steel or other metal possessing high tensile strength because they serve to flatten the shock wave generated by the explosive charge 13. The function of the discs 14 is to apply, upon detonation of charge 13, a compressive load to the piezoelectric element 15 which may be of any suitable material such as polarized barium titanate. In response to a compressive load applied thereto, element 15 generates an output voltage which is utilizable to actuate a plurality of detonators 19. These discs also serve to attenuate the shock wave so that the piezoelectric crystal will not be crushed, or destroyed, by the force of the explosion before a detonating voltage is generated thereby. The piezoelectric crystal I5 is sandwiched between two lead discs 16 which are relatively pliant or plastic at the pressures created by the explosion of charge 13 so that the compressive load is uniformly distributed over the face of the piezoelectric element.

These lead discs may be replaced by any of several expedients, for example, by a fluid in a yieldable container, a gel, a porous medium or any of several combinations of these elements and are shown as lead discs merely for the purpose of illustration. A stationary steel block 17 constrains the piezoelectric crystal 15 in position when the explosive charge 13 is initiated so that the maximum voltage may be generated across the faces 31 and 32 of the crystal while a resistor 18 is connected across the faces of the piezoelectric crystal to prevent accidental initiation of the detonator by a voltage generated by inertial loading of the crystal. The time constant of this shunting resistor circuit must be appreciably greater than the time it takes for the piezoelectric element to generate the maximum output voltage when a compressive load is supplied to the crystal by the explosion of charge 13 and yet be sufficiently short so that any spurious voltages generated by accidental disturbance of the piezoelectric element 15 will be shorted between the faces of the crystal and will not build up across the detonators 19. It has been determined that when used with a typical crystal, the value of resistor 18 should be at least 25,000 ohms and preferably in the neighborhood of 50,000 ohms. As shown in FIG. 1, a plurality of detonators 19 are connected across the faces of the piezoelectric crystal 15. Each detonator 19 is connected in series with a current limiting resistor 29 which prevents dissipation of too large a fraction of the available energy in the event that one of the detonators should break down prematurely. While the detonators are shown connected in parallel across the face of the crystal, they may also be fired in series if it is desired. The detonators 19 are distributed throughout the bulk of a main destructive explosive charge (not shown) so that simultaneous actuation of the detonators results in simultaneous ignition of the destructive charge at a multitude of points, namely the points where the detonators are positioned.

As shown in FIG. 2, the detonators 19 are each composed of a conductive casing, cylinder or a sleeve 21 which is electrically connected to face 31 of the crystal 15, i.e. ground potential. An electrical lead wire 22 is disposed within one end of the sleeve 21 and is electrically insulated therefrom by insulating plug 23. Lead 22 is adapted to be connected to one end of a resistor 29 of which the other end is connected to face 32 of crystal 15. A first layer of explosive material 24 abuts the end of the electrical lead-in wire 22 and is contiguous to the plug 23. This explosive layer must possess a selected dielectric strength so that when an electric pulse is applied between the sleeve 21 and the electrical lead-in wire 22, the explosive layer 24 breaks down electrically causing a spark which initiates this layer of explosive. A mixture of silver azide with about per cent 1 percent carbon is preferably used as the material in this layer because the breakdown voltage of this mixture is not so high that it exceeds the voltage generated by the common types of piezoelectric crystals and yet is sufficiently high so that the spark formed when the dielectric breaks down contains sufficient energy to initiate the mixture. A second explosive layer 25 is contiguous to the first explosive layer 24 and possesses greater explosive power than layer 24 and therefore magnifies the explosive force of layer 24. This layer may be silver azide without the aforedescribed carbon content. When initiated by the explosion of layer 24, layer 25 initiates the main detonator explosive 26 which requires a higher energy of initiation than either layer 24, or layer 25 and is preferably composed of subsieve RDX. The layer 26 explodes with sufficient energy to detonate the main explosive charge (not shown) at one point.

As an optional safety feature, an arming bridge wire 27 is connected between sleeve 21 and the electrical lead-in wire 22 to act as a fuse and short circuit the detonator for low voltages. This bridge wire 27 is burned off or destroyed by the application of a current of sufficient energy; the composition and physical dimensions of the wire are selected so that it requires a current of relatively high energy to burn it off. At the same time, the voltage necessary to destroy wire 27 is much lower than that required to initiate its corresponding detonator 19 so that the firing of the detonator can be accomplished by first applying high energy, low voltage pulse to the detonator circuit to burn off the wire 27 and arm the detonator. Since a large quantity of energy is required to burn off the arming wire, spurious transient voltages containing small amounts of energy will be shorted to the casing 21 and will not arm the detonator. When the detonator is ready for use, it is armed by connecting a battery B via switch 8 or other low voltage, high energy source to the circuit, there is no danger of premature initiation of the detonator during the arming cycle because the voltage output of the battery is selected to be less than the breakdown voltage of the dielectric explosive layer 24.

Assuming that the detonators 19 are in the armed condition as by rupture of fuse wires 27 as aforedescribed, the device operates in the following manner. An electric impulse is applied to the explosive initiator wire 12 which initiates explosive charge 13 driving the steel discs or plates to the right to a compressive load to the piezoelectric element 15 which in turn generates a voltage across its faces. Since the sleeves 21 of the detonators 19 are each connected to face 31 of element 15 and since the electrical lead-in wire 22 of the detonators are connected through resistors 29 to the face 32 of the crystal, virtually the entire potential generated appears between each wire and its respective sleeve. Almost instantaneously, this potential exceeds the breakdown value of the explosive layer 24 causing a discharge between the lead-in wire 22 and the sleeve 21 of sufficient energy to initiate the explosive layer 24 which in turn controls the explosive layers 25 and 26 to detonate the main charge. It is to be understood that the several detonators 19 are selectively placed or positioned around the main explosive charge in such a manner as to obtain any desired shape of the detonating wave front.

While this system has been shown in but one preferred embodiment, it should be apparent to those skilled in the art that it is not so limited but is susceptible of many modifications and alterations without departing from the spirit or scope of this invention. Therefore the specification should be construed as illustrative and not as limiting this invention in any manner.

What I claim as new and desired to be secured by letters Patent of the United States is:

l. A system for controlling the geometry of a detonation shock wave applied to an explosive charge which comprises; a piezoelectric element having first face and a second face and adapted to generate a voltage between said faces when stressed, explosive actuated means for applying a substantially instantaneous uniform compressive load to said element to produce a rapidly developing output voltage between said first face and said second face, a shunting resistor connected between said faces to short circuit slowly developing voltages, a plurality of electroresponsive detonators also connected across the first face and the second face, and a plurality of limiting resistors each connected in series with a respective one of said detonators to promote simultaneity of initiation of said detonators.

2. The system of claim 1 wherein the detonators are electrically connected in parallel.

3. A system for multiple point simultaneous initiation of an explosive which comprises; a piezoelectric element having a first face and a second face, said element being adapted to generate a voltage across said faces when compressed, means for rapidly impressing a compressive load on said element, said means comprising; a thick walled container open at one end, an explosive charge within said container, means for initiating said charge to create a shock wave, moveable means disposed over the open end of said container to flatten and attenuate the shock wave resulting from initiation of said charge, first pliant load distributing means associated with said last-named means and in abutting relation to a surface of said piezoelectric element, a relatively immovable block having a second pliant load-distributing means abutting a surface of said piezoelectric element opposite from the surface of said element in abutting relation to said first load-distributing element, whereby said element is uniformly compressed when said charge is initiated, a shunt resistor electrically connected between the first face and the second face of said piezoelectric element to short circuit spurious voltages generated by accidental compression of said element, and a plurality of electrically operated detonators connected between said faces for actuation by a voltage generated by rapid compression of said piezoelectric element.

4. A system for controlling the geometry of a detonation shock wave which comprises, a piezoelectric crystal having a first face and a second face and adapted to generate a voltage between the faces when stressed; means for rapidly stressing said crystal including a container having an opening at one end, an explosive charge substantially filling said container, means for initiating said charge, a plurality of load-applying discs movably disposed above the opening of said container and adapted to be forcibly driven away from said container upon initiation of said explosive charge, a first load-distributing member connected to said discs and abutting said piezoelectric crystal, and an immovable block having a second load distributing member abutting a surface of said crystal remote from said first load-distributing member to uniformly stress said crystal upon the forcible movement of said discs; a plurality of detonators connected between the first face and the second face of said crystal and initiated by rapid stressing of said crystal, each of said detonators comprising a hollow casing having at least an electrically conducting portion connected to the first face of said piezoelectric crystal and a plurality of layers of explosives within said casing, said layers including a first explosive layer of a preselected dielectric strength disposed contiguous to the electrically conducting portion of said casing and a second explosive layer having a higher initiation point than said first layer and controlled by initiation of said first layer to initiate the main explosive charge at one point; and a wire connected to the second face of said piezoelectric crystal and disposed within said container, said wire being contiguous to said first explosive layer and remote from the conducting portion of said casing whereby a voltage exceeding the dielectric strength of said first layer is impressed across said first layer to cause a spark discharge sufficient to initiate said first explosive layer when said crystal is stressed.

5. An electroresponsive detonator for detonating an explosive charge, comprising; a hollow electrically conducting casing, a plurality of explosive layers within said casing, said layers including a first explosive layer requiring a low energy for initiation thereof and having a predetermined high breakdown potential characteristic, and a second explosive layer disposed within said casing and connected to receive said detonating voltage from said means, said wire being electrically insulated from said container and in contact with said first explosive layer whereby an arc discharge is formed within said first explosive layer between said wire and said casing to initiate said first explosive layer in response to said detonating voltage a fusible wire connecting said first wire to said casing to short and disarm the detonator, low-potential high-energy generating means for connection to said fusible wire to fuse it and arm the detonator without exceeding the high breakdown potential of said first wire.

6. The detonator of claim 5 wherein the first explosive layer comprises a mixture of silver azide and a small percent of carbon,

7. An electrically actuated detonator for initiating an explosive charge which comprises an electrically conducting casing, a plurality of sequentially initiated layers of explosive material within said casing and including a first initiated layer of explosive material requiring a relatively low energy, high voltage initiation spark and having a dielectric strength at least equal to its initiation voltage, the last initiated layer having an explo: sive magnitude sufficient to detonate the charge, piezoelectric means having a first output terminal and a second output terminal and being operable to generate a voltage exceeding the breakdown potential of said first layer, means connecting said first terminal to said casing, electrically conducting means disposed within said casing and electrically connected to said second terminal, said electrically conducting rrieans being in electrical contact with said first layer of explosive layer of explosive material, a fusible, electrically conducting arming wire connecting said casing and said last-named electrically conducting means to prevent accidental initiation of the detonator, low voltage, high energy current-generating means associated with said arming wire to fuse said wire and break the electrical contact between said casing and said electrically conducting means whereby a voltage exceeding the dielectric strength of said first layer of explosive material is impressed across said layer upon generation of a detonating voltage by said piezoelectric means. I

8. The detonator of claim 7 wherein the first initiated layer of explosive is silver azide with a small amount of carbon.

9. In combination, a piezoelectric element for generating an electrical output having a definite characteristic when said element is uniformly compressed, explosive means, force distributing means adjacent to said explosive means for actuation thereby and abutting said element for effecting uniform compression of said element upon ignition of said explosive means, electroresponsive means connected to said element for actuation by the electrical output, and an electrical output characteristic discriminating resistor shunted across said electroresponsive means for rendering said electroresponsive means sensitive only to electrical outputs characteristic of said element. 

1. A system for controlling the geometry of a detonation shock wave applied to an explosive charge which comprises; a piezoelectric element having first face and a second face and adapted to generate a voltage between said faces when stressed, explosive actuated means for applying a substantially instantaneous uniform compressive load to said element to produce a rapidly developing output voltage between said first face and said second face, a shunting resistor connected between said faces to short circuit slowly developing voltages, a plurality of electroresponsive detonators also connected across the first face and the second face, and a plurality of limiting resistors each connected in series with a respective one of said detonators to promote simultaneity of initiation of said detonators.
 2. The system of claim 1 wherein the detonators are electrically connected in parallel.
 3. A system for multiple point simultaneous initiation of an explosive which comprises; a piezoelectric element having a first face and a second face, said element being adapted to generate a voltage across said faces when compressed, means for rapidly impressing a compressive load on said element, said means comprising; a thick walled container open at one end, an explosive charge within said container, means for initiating said charge to create a shock wave, moveable means disposed over the open end of said container to flatten and attenuate the shock wave resulting from initiation of said charge, first pliant load distributing means associated with said last-named means and in abutting relation to a surface of said piezoelectric element, a relatively immovable block having a second pliant load-distributing means abutting a surface of said piezoelectric element opposite from the surface of said element in abutting relatIon to said first load-distributing element, whereby said element is uniformly compressed when said charge is initiated, a shunt resistor electrically connected between the first face and the second face of said piezoelectric element to short circuit spurious voltages generated by accidental compression of said element, and a plurality of electrically operated detonators connected between said faces for actuation by a voltage generated by rapid compression of said piezoelectric element.
 4. A system for controlling the geometry of a detonation shock wave which comprises, a piezoelectric crystal having a first face and a second face and adapted to generate a voltage between the faces when stressed; means for rapidly stressing said crystal including a container having an opening at one end, an explosive charge substantially filling said container, means for initiating said charge, a plurality of load-applying discs movably disposed above the opening of said container and adapted to be forcibly driven away from said container upon initiation of said explosive charge, a first load-distributing member connected to said discs and abutting said piezoelectric crystal, and an immovable block having a second load distributing member abutting a surface of said crystal remote from said first load-distributing member to uniformly stress said crystal upon the forcible movement of said discs; a plurality of detonators connected between the first face and the second face of said crystal and initiated by rapid stressing of said crystal, each of said detonators comprising a hollow casing having at least an electrically conducting portion connected to the first face of said piezoelectric crystal and a plurality of layers of explosives within said casing, said layers including a first explosive layer of a preselected dielectric strength disposed contiguous to the electrically conducting portion of said casing and a second explosive layer having a higher initiation point than said first layer and controlled by initiation of said first layer to initiate the main explosive charge at one point; and a wire connected to the second face of said piezoelectric crystal and disposed within said container, said wire being contiguous to said first explosive layer and remote from the conducting portion of said casing whereby a voltage exceeding the dielectric strength of said first layer is impressed across said first layer to cause a spark discharge sufficient to initiate said first explosive layer when said crystal is stressed.
 5. An electroresponsive detonator for detonating an explosive charge, comprising; a hollow electrically conducting casing, a plurality of explosive layers within said casing, said layers including a first explosive layer requiring a low energy for initiation thereof and having a predetermined high breakdown potential characteristic, and a second explosive layer controlled by the initiation of said first layer and developing sufficient energy upon initiation thereof to detonate the charge, means generating a detonating voltage greater than the breakdown potential of said first layer, a first wire disposed within said casing and connected to receive said detonating voltage from said means, said wire being electrically insulated from said container and in contact with said first explosive layer whereby an arc discharge is formed within said first explosive layer between said wire and said casing to initiate said first explosive layer in response to said detonating voltage a fusible wire connecting said first wire to said casing to short and disarm the detonator, low-potential high-energy generating means for connection to said fusible wire to fuse it and arm the detonator without exceeding the high breakdown potential of said first wire.
 6. The detonator of claim 5 wherein the first explosive layer comprises a mixture of silver azide and a small percent of carbon.
 7. An electrically actuated detonator for initiating an explosive charge which comprises an electrically conducting caSing, a plurality of sequentially initiated layers of explosive material within said casing and including a first initiated layer of explosive material requiring a relatively low energy, high voltage initiation spark and having a dielectric strength at least equal to its initiation voltage, the last initiated layer having an explosive magnitude sufficient to detonate the charge, piezoelectric means having a first output terminal and a second output terminal and being operable to generate a voltage exceeding the breakdown potential of said first layer, means connecting said first terminal to said casing, electrically conducting means disposed within said casing and electrically connected to said second terminal, said electrically conducting means being in electrical contact with said first layer of explosive layer of explosive material, a fusible, electrically conducting arming wire connecting said casing and said last-named electrically conducting means to prevent accidental initiation of the detonator, low voltage, high energy current-generating means associated with said arming wire to fuse said wire and break the electrical contact between said casing and said electrically conducting means whereby a voltage exceeding the dielectric strength of said first layer of explosive material is impressed across said layer upon generation of a detonating voltage by said piezoelectric means.
 8. The detonator of claim 7 wherein the first initiated layer of explosive is silver azide with a small amount of carbon.
 9. In combination, a piezoelectric element for generating an electrical output having a definite characteristic when said element is uniformly compressed, explosive means, force distributing means adjacent to said explosive means for actuation thereby and abutting said element for effecting uniform compression of said element upon ignition of said explosive means, electroresponsive means connected to said element for actuation by the electrical output, and an electrical output characteristic discriminating resistor shunted across said electroresponsive means for rendering said electroresponsive means sensitive only to electrical outputs characteristic of said element. 